Vaporizing sulfur from ore by direct contact with heated pebbles

ABSTRACT

THE CONTINUOUS METHOD OF AND APPARATUS FOR RECOVERING SULFUR FROM ORES BY FEEDING SURFACE SULFUR ORE INTO A CLOSED CONVEYOR AND SIMULTANEOUSLY HEATING THE ORE WITH HEATED PEBBLES WHILE SLOWLY MIXING AND CONVEYING THE MIXTURE THROUGH THE CONVEYOR AND HEATING THE ORE ABOVE THE BOILING POINT OF SULFUR TO VAPORIZE THE SULFUR IN WHICH THE VAPORIZED SULFUR IS PASSED THROUGH A CONDENSER FOR RECOVERY. THE DEPLETED ORE AND PEBBLES ARE DISCHARGED FROM THE CONVEYOR AND SEPARATED WITH THE PEBBLES BEING CONVEYED TO A HEATER FOR REHEATING AND REUSE. FOR GREATER EFFICIENCY THE HOT EXHAUST GASES FROM THE PEBBLE HEATER ARE FLOWED IN A COUNTERFLOW HEAT EXCHANGE RELATIONSHIP WITH THE CONTAINER TO HEAT THE MIXTURE. THE CONVEYOR HAVING AN ELONGATE POWER SHAFT POSITIONED LONGITUDINALLY IN THE CONTAINER FOR ROTATIVE MOVEMENT WITH A PLURALITY OF PADDLES POSITIONED ADJACENT THE INTERIOR WALLS OF THE CONTAINER AND CONNECTED BY THE SHAFT FOR ROTATIVE MOVEMENT TO MIX THE ORE AND PEBBLES, MOVE THE MIXTURE ALONG THE CONVEYOR, AND KEEP THE INTERIOR WALLS OF THE CONTAINER CLEANED FOR GREATER HEAT TRANSFER. THE VOLUME OF PEBBLES BEING GREATER THAN THE VOLUME OF ORE IN THE CONTAINER TO MORE EASILY CONVEY THE MIXTURE THROUGH THE CONVEYOR.   D R A W I N G

May 11, 1971 J, M, DALE VAPORIZING SULFUR FROM ORE BY DIRECT CONTACTWITH HEATED PEBBLES Filed June 30. 1969 .A AmANw ATTOR/V'VJ UnitedStates Patent Office n3,578,417 Patented May 1l, 1971 U.S. Cl. 23--29411 Claims ABSTRACT OF THE DISCLOSURE The continuous method of andapparatus for recovering sulfur from ores by feeding surface sulfur oreinto a closed conveyor and simultaneously heating the ore with heatedpebbles while slowly mixing and conveying the mixture through theconveyor and heating the ore above the boiling point of sulfur tovaporize the `sulfur in which the vaporized sulfur is passed through acondenser for recovery. The depleted ore and pebbles are discharged fromthe conveyor and separated with the pebbles being conveyed to a heaterfor reheating and reuse. For greater eiciency the hot exhaust gases fromthe pebble heater are iiowed in a counterflow heat exchange relationshipwith the container to heat the mixture. The conveyor having an elongatepower shaft positioned longitudinally in the container for rotativemovement with a plurality of paddles positioned adjacent the interiorwalls of the container and connected by the shaft for rotative movementto mix the ore and pebbles, move the mixture along the conveyor, andkeep the interior walls of the container cleaned for greater heattransfer. The volume of pebbles being greater than the volume of ore inthe container to more easily convey the mixture through the conveyor.

BACKGROUND OF THE INVENTION The recovery of sulfur from sulfur ores thatlie on or near the surface cannot be mined by the Frasch process.

In spite of the large amount of known sulfur reserves in such surfaceores a lack of commercial exploitation of these ores has occurredbecause of a problem of economics as well as a problem in processing.

However, the recent increase in the market price of sulfur has increasedthe potential economic attractiveness of these largely heretoforeuntapped sulfur reserves. Various processes such as flotation,autoclaving, solvent extraction and others have been attempted, but havebeen largely unsuccessful. The present process and apparatus is directedto the thermal process of recovering sulfur and operates on theprinciple of heating an ore containing sulfur to a high enoughtemperature so the sulfur will be vaporized and driven off. The thermalprocess avoids many of the disadvantages of other processes.

SUMMARY The present invention is directed to a -method of and anapparatus for recovery of sulfur from surface ores in which the ore isfed into a closed conveyor and mixed with heated pebbles in which theheat from the pebbles raises the ore temperature to above the boilingpoint of the sulfur creating sulfur vapors which are passed to acondenser and the sulfur recovered. The depleted ore and pebbles aredischarged from the conveyor and are separated with the pebbles beingconveyed to a pebble heater where they are reheated and reused.

Another feature of the present invention is the provision of utilizingthe exhaust heat from the pebble heater which is passed in a counterflowheat exchange relationship with the conveyor for additionally heatingthe mixture therein.

Another feature of the present invention is the provision of mixing avolume of pebbles greater than the volume of ore in the conveyor, andpreferably as much as three or four times greater in order to insurethat the mixture can be satisfactorily moved by the conveyor sincesulfur becomes quite viscous when heated.

A still further feature of the present invention is the provision of aconveyor which mixes the heated pebbles and ore suiciently to vaporizethe sulfur in the ore, but slowly enough so as not to churn up dustwhich might be carried out with the vapors, and additionally theconveyor removes material from the internal walls of the conveyorcontainer for improving the heat transfer from the pebble heater exhaustgases into the conveyor.

A still further object of the present invention is the provision of aprocess and apparatus for recovering sulfur from surface ores in whichthe ore is fed through an air lock into a container and heated pebblesare heated above the boiling point of sulfur and inserted through an airlock and into the container in which an elongate power shaft ispositioned longitudinally for rotative movement with a plurality ofpaddles positioned adjacent the interior walls of the container andconnected to the shaft for mixing the pebbles and ore together andconveying the mixture along the container and a condenser is connectedto the container for receiving the vaporized sulfur from the containerand condensing the sulfur and having an outlet from the container forremoving the depleted ore and pebbles with means for separating thepebbles from the depleted ore and may be returned to the heater andreused. In addition, the exhaust gas from the pebble heater may bereused to preheat the pebbles which have been separated from thedepleted ore.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of theschematic of the flow process and apparatus of the present invention,and FIG. 2 is a view taken along the line 2 2 of FIG. l.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsand particularly to FIG. 1, the reference numeral 10 generally indicatesan apparatus for recovering sulfur and generally includes a container 12having a conveyor 14 therein, a pebble heater 16, and a condenser 18.

The container 12 is a closed container having an ore inlet line 20 whichadmits surface sulfur ore from a suitable source such as from a storagebin 22 through a conventional air lock 24` The ore in the storage bin 22is surface ore which has been ground up prior to storage in bin 22,which normally contains approximately 30% by Weight of elemental sulfur,from which it is desired to extract the sulfur. A pebble inlet line 26is provided to the container 12 through a conventional air lock 28 fromthe pebble heater 16 through which pebbles have been fed, such as bygravity. An outlet line 30 from the container 12 is provided through anair lock 32 for removing the mixture of depleted ore and pebbles afterprocessing. Thus, the closed container 12 prevents any air or oxygenfrom entering the system thereby avoiding any undesirable igniting andburning of the sulfur therein.

The pebble heater 16 may be any suitable and conventional heater, suchas a rotary direct tired heater, which is supplied with a fuel, such asgas, from line 34 to heat the heat carrying pebbles to a temperatureabove the boiling point of sulfur, 832 F., and as high as thermallyefiicient, such as 2500 F., and preferably to an approximate temperatureof 2200 F. The heat carrying pebbles may be of any suitable materialsuch as stainless steel or ceramic and may be of any convenient size,for example 2 inches in diameter. The heated pebbles flow through theair lock 28 and inlet line 26 to the container 12 to raise thetemperature of the mixture to above the boiling point of the sulfurwhereby the sulfur is driven off as a vapor.

Preferably, the conveyor 14 includes an elongate power shaft 36positioned longitudinally in the container 12 for rotative movement byany suitable means (not shown) and includes a plurality of paddles 38positioned adjacent the interior walls of the container 12 and connectedto the shaft 36 by radially extending arms 40. The paddles 38 are slowlyrotated, for example only, one revolution per two minutes, to thoroughlymix the mixture of heated pebbles and the ore to drive off the sulfurfrom the ore, but slowly enough so as not to churn up dust from the orewhich might be carried out with the sulfur vapors and contaminate thesulfur. Additionally, the paddles 38 include a slanted portion 42 on theleading edges of the paddles whereby the mixture of the heated pebblesand ore are moved by the paddles from the inlets 20 and 26 toward theoutlet 30'.

A still further function of the paddles 38 is to scrape the materialadjacent the interior walls of the container 12 for increasing heattransfer into the container 12. That is, the exhaust or flue gases fromthe pebble heater 16 ow through heater exhaust line 44 and through aheat exchange manifold 46 which is positioned in a counterflow heatexchange relationship with the exterior of the container 12, here shownas enclosing the container 12, to provide additional heat for heatingthe mixture in the container 12. However, the sulfur in the mixtureadjacent the interior wall of the container 12 on vaporization leaves asulfur free dry powdery gangue which acts as an insulator and retardsfurther transfer of heat to the mass of the mixture. The action of thepaddles 38 adjacent the interior walls 13` of the container 12 scrapesand destroys this insulation layer so that heat from the manifold 46 maybe more easily transferred through the wall of the container 12 and intothe mixture by improving the heat transfer coefficient.

Two difficulties arise in processing sulfur ores. When the ore is heatedto just above the melting point of sulfur, 238 F., the liquid sulfurforms a paste with the gangue. Above 320 F., sulfur becomes extremelyviscous and makes the material (or paste like mixture) even moredifficult to handle. These difficulties are overcome in the presentprocess by mixing the pebbles with the ore in the container 12. Thus,the volume of pebbles inserted into the container is greater than thevolume of ore, and preferably the ratio of volume of pebbles to ore isthree or four to one. With a greater portion of the mass in thecontainer being formed of the pebbles, the mass can satisfactorily bemoved by the conveyor 14. Also, because of these properties of sulfur,it is desirable that the pebble inlet 26 be located adjacent to the oreinlet 20, or if desired, even upstream from the ore inlet 20 to insurethat the pebbles may be mixed with the ore to avoid clogging up theconveyor 14.

Sulfur vapor outlets S are provided connected to the container 12 forallowing passage of the sulfur vapors which are driven off from theheated mixture to pass through vapor line 52 and a gas cleaningapparatus 51, if desired, such as a cyclone or electrostatic cleaner toremove contaminants, to a conventional sulfur vapor condenser 18 whichmay be air or water cooled wherein the sulfur vapors are recovered asliquid sulfur from condenser outlet 54,

The sulfur depleted ore and pebbles are discharged from the container 12through the outlet 30 and air lock 32 to suitable means for removing thepebbles from the depleted ore such as screen 56. The depleted ore organgue are discharged through an outlet 58 and discarded. The separatedpebbles 11 are fed back to the pebble heater 16, such as through asuitable pebble elevator 60, for reheating and reuse and thereforeoperate in a closed loop circuit. And if desired, the exhaust gas outlet44 from the pebble heater 16 may form a heat exchanger 62 with theelevator `60 to preheat the pebbles prior to their entry into the heater16 from elevator outlet 64.

In operation, ground up surface sulfur ore is continuously fed throughair lock 24 and inlet 20, such as from a bin storage 22, into thecontainer 12. Simultaneously, pebbles Which are heated in the heater 16are continuously fed through air lock 28 through pebble inlet 26 intothe container 12 where they are mixed by the conveyor 14 by the actionof the paddles 38 to heat the mixture above the boiling point of 832 F.of the sulfur driving off the sulfur as vapors. The mixture of pebblesand ore is moved through the container 12 continuously by the conveyor14 and additional heat may be supplied from the flue gases from theheater 16 flowing through the heating manifold 46 from line 44. Thesulfur vapors are passed through outlets 50 through line 52 to thesulfur condenser 18 where the sulfur is recovered as a liquid fromoutlet 54. The depleted ore and pebbles are discharged from thecontainer 12 through outlet 30 and air lock 32 to separation means suchas a screen 56 with the depleted ore being discarded through outlet 58and the pebbles being conveyed again to the heater 16 such as byelevator 60 for reheating and reuse. The present process and apparatusoperates on a continuous cycle of heating the sulfur ore to a highenough temperature so that the sulfur will be vaporized and driven offwithout involving the disadvantages in other sulfur recovery processes.

It is believed that the process of the present invention is apparentfrom the foregoing description of a presently preferred apparatus of theinvention. The process, however, comprises the steps of feeding a sulfurore into a container and preventing air from entering the container,heating heat carrying pebbles to a temperature greater then the boilingpoint of sulfur, feeding the heated pebbles into the container and theore whereby the ore is heated and the sulfur is vaporized, removing thevaporized sulfur to a condenser for recovering the sulfur, removing thedepleted ore and the pebbles from the container, and separating thepebbles from the depleted ore for reuse. The process also comprehendsheating' the pebbles in the range of from greater than 832 F. to 2500@F., slowly mixing the heated pebbles with the ore to thoroughly heat themixture without creating undesirable dust in the container. The processfurther includes the step of removing material from the internal wallsof the container as heat is supplied to the external surface of thecontainer from exhaust from the pebble heater to increase heat transferinto the container. The process further comprehends inserting a greatervolume of pebbles into the container than the volume of ore insertedtherein to reduce the viscosity of the mixture for ease of conveyancethrough the container.

The present invention, therefore, is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as othersinherent therein.

What is claimed is: 1. The continuous method of recovery of sulfur fromores comprising,

feeding the ore into an elongate container, preventing air from enteringthe container, heating heat carrying pebbles to a temperature greaterthan the boiling point of sulfur and in the range of from above about862 F. to about 2500 F.,

feeding the heated pebbles into the container and into the ore wherebythe ore is heated and the sulfur is vaporized, passing the mixture ofore and pebbles concurrently through said container while agitating themixture,

removing the vaporized sulfur from said container to a condenser forrecovering the sulfur,

removing the depleted ore and the pebbles from the container, and

separating the pebbles from the depleted ore for reuse.

2. The process of claim 1 wherein the ore and heated pebbles are mixedas they are moved through the container but are mixed slowly to preventundesired dust from the ore from mixing with the vaporized sulfur.

3. The process of claim 1 wherein the exhaust heating gas from heatingthe pebbles flows in a heat exchange relationship with the outside ofthe container heating the mixture of ore and pebbles.

4. The process of claim 1 wherein the heated pebbles are fed into thecontainer adjacent the point of admittance of the ore into thecontainer.

5. The process of claim 1 wherein the volume of pebbles inserted intothe container are greater than the volume of ore inserted into thecontainer.

6. The continuous process of recovery of sulfur from ores comprising,

feeding the ore into a substantially horizontal elongated container,preventing air from entering the container, heating heat carryingpebbles to a temperature in excess of the boiling point of sulfur and inthe range of from above about 862 F. to about 2500 F.,

inserting the heated pebbles into the ore in the container whereby theore is heated and the sulfur is vaporized,

mixing the ore and pebbles in the container,

moving the ore and pebbles along the container,

removing the vaporized sulfur from the container to a condenser forrecovering the sulfur,

removing the depleted ore and pebbles from the container,

separating the pebbles from the depleted ore for reuse.

7. The process of claim 6 wherein the volume of pebbles inserted intothe container is greater than the volume of ore.

8. The process of claim 6 wherein the exhaust heating gas from heatingthe pebbles ows in a counterow, with respect to the direction of iiow ofthe ore and pebbles through the container, heat exchange relationshipwith the outside of the container for heating the mixture in thecontainer.

9. The process of claim 8 including removing material from the internalwalls of the container for improving the heat transfer through thecontainer.

10. The process of claim 1 wherein the exhaust heating gas from heatingthe pebbles ilows in a counterflow, with respect to the direction of owof the ore and pebbles through the container, heat exchange relationshipwith the outside of the container heating the mixture in the container.

11. The process of claim 10 including removing material from theinternal walls of the container for improving the heat transfer throughthe container.

References Cited UNITED STATES PATENTS Re. 23,318 1/1951 Porter 23-294X1,535,468 4/1925 Hedges 23-294 1,614,387 1/1927 Pereda 165-107 1,782,22511/1930 Bacon 23-227 1,900,667 3/ 1933 Raloer 23-227X 1,946,349 2/1934Brown 23-227X 2,420,376 5 1947 Johansson 263-19B 2,63 6,723 4/1953Harter 26S-19B 2,872,386 2/1959 Aspegren 26S-19B 2,877,100 3/ 1959Hartley 23-227X 3,068,091 12/1962 Kirkland 75-36 3,102,792 9/1963 Eads23-294 FOREIGN PATENTS 353,830 5/1905 France.

NORMAN YUDKOFF, Primary Examiner S. J. EMERY, Assistant Examiner U.S.Cl. X.R.

